"Hot Karl" is a slang term for sex which involves feces. Such variations of a "Hot Karl" are having a bowel movement in your partner's mouth, the female partner giving the male partner fellatio after he has had anal sex with her, or when a parter has a bowel movement on the other partners stomach (usually, the partner getting boweled on has Saran Wrap on his/her stomach).

My wife and I experimented with the Hot Karl, wow do I love the taste of my woman's shit.

The Urban Dictionary Mug

When you getting a peice of cling wrap and cutting a whole in it for the lucky persons mouth. Then place the cling wrap over her face and release your feaces onto the cling wrap so that the girl can feel the warmth of the feaces through the cling wrap without coming into contact with the feaces

After the party this kinky girl let me hot karl.

After my roomate fell asleep me and my friends all hotkarled him and he threw up.